It is common practice to plow roadways by a plow blade mounted on the front of a motor vehicle. One of the most common type of mounting arrangements for a plowing blade is that used by individuals on their personal trucks or four wheel drive vehicles. The blade is mounted on a curved steel member known as a "sector" and is adapted to oscillate in either direction along a supporting frame known as an A-frame. By providing an upper arm pivoted by a hydraulic cylinder, a chain extending from the arm downwardly toward the A-frame can be used to selectively lift the A-frame, sector and plow blade in unison into the non-plowing position. By releasing the pressure on the cylinder, the weight of the blade itself moves the A-frame, sector and blade downwardly until the lower edge of the plow blade engages the roadway surface. This is the lowered plowing position of the blade. This mounting mechanism is relatively inexpensive, has been used for many years and is quite well known as a reliable arrangement for converting a vehicle into a device for clearing snow and other debris from roadways.
For municipal applications, larger plow blades are used on heavier trucks to perform heavy duty removal of snow. Such applications have resulted in a variety of mounting mechanisms for moving the plow blade from its raised position to its lowered plowing position. These mechanisms have been especially engineered, are low production and are costly. Attempts to use, for municipal plowing, the relatively inexpensive, simple and well tested personal type of blade mounting and lifting concepts utilizing an A-frame pulled upwardly for lifting a plow blade have not been successful. One of the basic disadvantages is caused by the relatively large size of plow blades used for such municipal plowing. When this blade is pivoted upwardly on an A-frame, it tends to obstruct the vision of the driver operating the motor vehicle. This is pronounced when the blade is angled to one side or the other which is the normal condition for plowing roadways. Also, the raised position of the large blade is quite high to provide clearance when the plowing operation is not being performed. This high, raised position causes instability of the vehicle and substantial strain on the mounting arrangement. For these reasons, the standard individual blade mounting mechanism has not been widely adopted by municipal plowing operators. Consequently, special low production, high cost mounting devices are generally used for municipal plowing vehicles.